The invention relates to a continuously variable belt-drive mechanism, particularly for motor vehicles, with at least one variator. The term "variator" as used herein means a pulley comprised of at least two conical disks arranged concentrically on a driving shaft of a prime mover unit or on an element that is connected to the driving shaft. At least one of the conical disks is axially movable, and an endless flexible torque-transmitting device (subsequently referred to as a belt) occupies the axial space between the conical disks at a location of variable radius. A disk-tightening device pushes the conical disks axially towards each other so that, by virtue of the frictional engagement between the conical disks and the belt, the latter receives the torque to be transmitted and passes it on to at least one pulley disk.
Continuously variable belt-drive mechanisms of this kind are used in particular in motor vehicles as continuously variable transmissions and as drivers of auxiliary devices. In transmitting torque from the variator to other pulley disks, the critical factor is the frictional engagement between the belt and the conical disks. The disk-tightening devices used to produce the frictional engagement are in many cases energy-storing elements, such as helix springs, pushing against the axially movable conical disks. However, with an arrangement of this kind, the contact pressure between the belt and the conical disks is independent of the amount of torque that is to be transmitted.
Also known are variators with disk-tightening devices in which the amount of contact pressure depends on a centrifugal force, i.e., increases at greater rpm speeds, whereby the contact pressure is only coarsely adapted to the amount of torque that is to be transmitted.
In DE-OS 35531830, a disk-tightening device is proposed where the conical disks are pushed against a belt by a torque-dependent force. The conical disks are moved by pull rods with pivotal connections at both ends that are expensive to manufacture. Besides the cost factor, the proposed disk-tightening device also requires a great amount of space in the axial dimension.